Re: [PATCH v8 2/6] module: allow symbol exports to be disabled
On Sun, 11 Mar 2018, Ard Biesheuvel wrote:
> To allow existing C code to be incorporated into the decompressor or
> the UEFI stub, introduce a CPP macro that turns all EXPORT_SYMBOL_xxx
> declarations into nops, and #define it in places where such exports
> are undesirable. Note that this gets rid of a rather dodgy redefine
> of linux/export.h's header guard.
>
> Signed-off-by: Ard Biesheuvel
Acked-by: Nicolas Pitre
> ---
> arch/x86/boot/compressed/kaslr.c | 5 +
> drivers/firmware/efi/libstub/Makefile | 3 ++-
> include/linux/export.h| 11 ++-
> 3 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c
> b/arch/x86/boot/compressed/kaslr.c
> index 8199a6187251..3a2a6d7049e4 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -23,11 +23,8 @@
> * _ctype[] in lib/ctype.c is needed by isspace() of linux/ctype.h.
> * While both lib/ctype.c and lib/cmdline.c will bring EXPORT_SYMBOL
> * which is meaningless and will cause compiling error in some cases.
> - * So do not include linux/export.h and define EXPORT_SYMBOL(sym)
> - * as empty.
> */
> -#define _LINUX_EXPORT_H
> -#define EXPORT_SYMBOL(sym)
> +#define __DISABLE_EXPORTS
>
> #include "misc.h"
> #include "error.h"
> diff --git a/drivers/firmware/efi/libstub/Makefile
> b/drivers/firmware/efi/libstub/Makefile
> index 7b3ba40f0745..896a882c89f4 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB)+=
> -I$(srctree)/scripts/dtc/libfdt
> KBUILD_CFLAGS:= $(cflags-y)
> -DDISABLE_BRANCH_PROFILING \
> -D__NO_FORTIFY \
> $(call cc-option,-ffreestanding) \
> -$(call cc-option,-fno-stack-protector)
> +$(call cc-option,-fno-stack-protector) \
> +-D__DISABLE_EXPORTS
>
> GCOV_PROFILE := n
> KASAN_SANITIZE := n
> diff --git a/include/linux/export.h b/include/linux/export.h
> index 1a1dfdb2a5c6..25005b55b079 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -72,7 +72,16 @@ extern struct module __this_module;
> __attribute__((section("___ksymtab" sec "+" #sym), used)) \
> = { (unsigned long)&sym, __kstrtab_##sym }
>
> -#if defined(__KSYM_DEPS__)
> +#if defined(__DISABLE_EXPORTS)
> +
> +/*
> + * Allow symbol exports to be disabled completely so that C code may
> + * be reused in other execution contexts such as the UEFI stub or the
> + * decompressor.
> + */
> +#define __EXPORT_SYMBOL(sym, sec)
> +
> +#elif defined(__KSYM_DEPS__)
>
> /*
> * For fine grained build dependencies, we want to tell the build system
> --
> 2.15.1
>
>
[PATCH v8 2/6] module: allow symbol exports to be disabled
To allow existing C code to be incorporated into the decompressor or
the UEFI stub, introduce a CPP macro that turns all EXPORT_SYMBOL_xxx
declarations into nops, and #define it in places where such exports
are undesirable. Note that this gets rid of a rather dodgy redefine
of linux/export.h's header guard.
Signed-off-by: Ard Biesheuvel
---
arch/x86/boot/compressed/kaslr.c | 5 +
drivers/firmware/efi/libstub/Makefile | 3 ++-
include/linux/export.h| 11 ++-
3 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 8199a6187251..3a2a6d7049e4 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -23,11 +23,8 @@
* _ctype[] in lib/ctype.c is needed by isspace() of linux/ctype.h.
* While both lib/ctype.c and lib/cmdline.c will bring EXPORT_SYMBOL
* which is meaningless and will cause compiling error in some cases.
- * So do not include linux/export.h and define EXPORT_SYMBOL(sym)
- * as empty.
*/
-#define _LINUX_EXPORT_H
-#define EXPORT_SYMBOL(sym)
+#define __DISABLE_EXPORTS
#include "misc.h"
#include "error.h"
diff --git a/drivers/firmware/efi/libstub/Makefile
b/drivers/firmware/efi/libstub/Makefile
index 7b3ba40f0745..896a882c89f4 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -20,7 +20,8 @@ cflags-$(CONFIG_EFI_ARMSTUB) +=
-I$(srctree)/scripts/dtc/libfdt
KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
-D__NO_FORTIFY \
$(call cc-option,-ffreestanding) \
- $(call cc-option,-fno-stack-protector)
+ $(call cc-option,-fno-stack-protector) \
+ -D__DISABLE_EXPORTS
GCOV_PROFILE := n
KASAN_SANITIZE := n
diff --git a/include/linux/export.h b/include/linux/export.h
index 1a1dfdb2a5c6..25005b55b079 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -72,7 +72,16 @@ extern struct module __this_module;
__attribute__((section("___ksymtab" sec "+" #sym), used)) \
= { (unsigned long)&sym, __kstrtab_##sym }
-#if defined(__KSYM_DEPS__)
+#if defined(__DISABLE_EXPORTS)
+
+/*
+ * Allow symbol exports to be disabled completely so that C code may
+ * be reused in other execution contexts such as the UEFI stub or the
+ * decompressor.
+ */
+#define __EXPORT_SYMBOL(sym, sec)
+
+#elif defined(__KSYM_DEPS__)
/*
* For fine grained build dependencies, we want to tell the build system
--
2.15.1
